Juju creates extra/redundant VMs when using MAAS vmhost as backing cloud

Some weird race condition between Juju's request towards MAAS causes multiple duplicate
VM hosts to be created when using MAAS as the backing cloud with a either KVM or LXC VM vhost configured.

Steps to reproduce:
------
1. Deploy MAAS 3.x
2. Add a LXC VM host/hypervisor to MAAS so that it will be used to spin up VMs
3. Bootstrap Juju 2.x/stable controller using MAAS as the backing cloud
4. Deploy multiple VMs using the LXC VM host, for example via:
    $ juju add-machine -n3

Expected result

The exact count of machines desired by the model or -n argument are spun up.

Actual result:

Redundant/errnoeous VMs are spun up (cheif-wolf, bright-wew, super-moose):

l+-------------+---------+----------------------+------+-----------------+-----------+
| NAME | STATE | IPV4 | IPV6 | TYPE | SNAPSHOTS |
+-------------+---------+----------------------+------+-----------------+-----------+
| bright-ewe | STOPPED | | | VIRTUAL-MACHINE | 0 |
+-------------+---------+----------------------+------+-----------------+-----------+
| chief-wolf | STOPPED | | | VIRTUAL-MACHINE | 0 |
+-------------+---------+----------------------+------+-----------------+-----------+
| deep-goose | RUNNING | 172.16.66.195 (eth0) | | VIRTUAL-MACHINE | 0 |
+-------------+---------+----------------------+------+-----------------+-----------+
| hip-goat | RUNNING | 172.16.66.219 (eth0) | | VIRTUAL-MACHINE | 0 |
+-------------+---------+----------------------+------+-----------------+-----------+
| steady-cat | RUNNING | 172.16.66.151 (eth0) | | VIRTUAL-MACHINE | 0 |
+-------------+---------+----------------------+------+-----------------+-----------+
| super-moose | STOPPED | | | VIRTUAL-MACHINE | 0 |
+-------------+---------+----------------------+------+-----------------+-----------+
| valued-drum | RUNNING | 172.16.66.207 (eth0) | | VIRTUAL-MACHINE | 0 |
+-------------+---------+----------------------+------+-----------------+-----------+

I haven't narrowed down what exactly causes this -- is Juju not getting a reply from MAAS
fast enough and sending duplicate create requests?